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The proposed removal of the remnants of a hydroelectric dam in the Muskegon River at Big Rapids, Michigan, will potentially affect flow of the river at the city's water intake system. Fifteen boreholes were augered in bottom sediments in the river just upstream from the dam relic, and streambottom profiles were made using ground-penetrating radar. Data from boreholes show that sediments captured by the dam foundation were deposited in two distinctly different sedimentary environments. Sediments that overlie the pre-dam channel surface consist of lacustrine clay, wood chips, silt, and sand. These lacustrine sediments are interbedded in a cyclical fashion, and they were deposited under low flow to stagnant water conditions during 1916-66, when a 17-foot-tall hydroelectric dam was in place. Demolition of the upper 13 feet of this dam in 1966 resulted in erosion of most of the lacustrine sediments, and subsequent deposition of coarser alluvium in the impoundment behind the remaining dam foundation. Lacustrine sediments are present in the active part of the stream channel and extend from the dam foundation to about 1,300 feet upstream. The composite thickness of lacustrine sediments and overlying coarser alluvium was determined from sediment cores collected from the boreholes. The volume of these sediments is estimated to be about 19,000 cubic yards.
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Coal in the Ferron Sandstone Member of the Mancos Shale of Cretaceous age has traditionally been mined by underground techniques in the Emery Coal Field in the southern end of Castle Valley in east-central Utah. However, approximately 99 million tons are recoverable by surface mining. Ground water in the Ferron is the sole source of supply for the town of Emery, but the aquifer is essentially untapped outside the Emery area. The Ferron Sandstone Member crops out along the eastern edge of Castle Valley and generally dips 2 ? to 10 ? to the northwest. Sandstones in the Ferron are enclosed between relatively impermeable shale in the Tununk and Blue Gate Members of the Mancos Shale. Along the outcrop, the Ferron ranges in thickness from about 80 feet in the northern part of Castle Valley to 850 feet in the southern part. The Ferron also generally thickens in the subsurface downdip from the outcrop. Records from wells and test holes indicate that the full thickness of the Ferron is saturated with water in most areas downdip from the outcrop area. Tests in the Emery area indicate that transmissivity of the Ferron sandstone aquifer ranges from about 200 to 700 feet squared per day where the Ferron is fully saturated. Aquifer transmissivity is greatest near the Paradise Valley-Joes Valley fault system where permeability has been increased by fracturing. Storage coefficient ranges from about 10 .6 to 10 -3 where the Ferron sandstone aquifer is confined and probably averages 5 x 10 -2 where it is unconfined.
Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.
The Yorktown Formation records paleoclimate conditions along the mid-Atlantic Coastal Plain during the mid-Piacenzian Warm Period (3.264 to 3.025 Ma), a climate interval of the Pliocene in some ways analogous to near future climate projections. To gain insight into potential near future changes, we investigated Yorktown Formation outcrops and cores in southeastern Virginia, refining the stratigraphic framework. We analyzed 485 samples for alkenone-based sea surface temperature (SST) and productivity estimates from the Holland and Dory cores, an outcrop at Morgarts Beach, Virginia, and the lectostratotype of the Yorktown Formation at Rushmere, Virginia, and analyzed planktonic foraminferal assemblage data from the type section. Using the structure of the SST record, we improved the chronology of the Yorktown Formation by establishing the maximum age ranges of the Rushmere (3.3–3.2 Ma) and Morgarts Beach (3.2–3.15 Ma) Members. SST values for these members average ~26 °C, corroborating existing sclerochronological data. Increasing planktonic foraminifer abundance, productivity, and species diversity parallel increasing SST over the MIS M2/M1 transition. These records constitute the greatest temporal concentration of paleoecological estimates within the Yorktown Formation, aiding our understanding of western North Atlantic temperature patterns, seasonality and ocean circulation during this interval. We provide a chronologic framework for future studies analyzing ecological responses to profound climate change.
The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. To explore theoretical colluvial wedge evolution, we develop a cellular automata model driven by the production and disturbance (e.g., bioturbative reworking) of mobile regolith and fault-scarp collapse. We consider both 90 and 60 ∘ dipping faults and allow the colluvial wedges to develop over 2000 model years. By tracking sediment transport time, velocity, and provenance, we classify cells into analogs for the debris and wash sedimentary facies commonly described in paleoseismic studies. High values of mobile regolith production and disturbance rates produce relatively larger and more wash-facies-dominated wedges, whereas lower values produced relatively smaller, debris-facies-dominated wedges. Higher lateral collapse rates lead to more debris facies relative to wash facies. Many of the modeled colluvial wedges fully developed within 2000 model years after the earthquake, with many being much faster when process rates are high. Finally, for scenarios with the same amount of vertical displacement, differently sized colluvial wedges developed depending on the rates of geomorphic processes and fault dip. A change in these variables, say by environmental change such as precipitation rates, could theoretically result in different colluvial wedge facies assemblages for the same characteristic earthquake rupture scenario. Finally, the stochastic nature of collapse events, when coupled with high disturbance, illustrates that multiple phases of colluvial deposition are theoretically possible for a single earthquake event.
No abstract available.
The goal of the shelf sediment dynamics component of STRATAFORM is to link sediment transport processes active on the continental shelf to the formation and preservation of event beds in shelf sediment deposits. An approach combining shelf sediment-transport models with high-resolution measurements of water-column and bed properties over periods from several months to several years allows us to make quantitative estimates of bed modification caused by sediment resuspension during episodic transport events. These modifications include erosion and deposition of bed material, formation of graded storm beds, and changes in small-scale bed surface morphology. The characteristics of the resulting “event bed” (thickness, grading, physical structures) are a function of flow and bed properties, depending on both temporal and spatial variations in sediment transport.
The distribution and deposition of sedimentary mercury in the Sudbury River were linked to an industrial complex (Nyanza site) that operated from 1917 through 1978. In two reservoirs just downstream from the Nyanza site, estimated rates of mercury accumulation increased markedly in the 1920s and 1930s, were greatest during 1976-1982, decreased within 5 years after industrial operations ceased, and have decreased further since capping of contaminated soil at the Nyanza site was completed in 1991. The most contaminated sediments were typically buried, yet the 0- to 1-cm stratum remained substantially contaminated in all cores. Mercury accumulating in the surficial, reservoir sediments was probably from continuing, albeit much lesser, inputs from the Nyanza site, whereas recent inputs to downstream wetland areas were attributed to recycling of sedimentary mercury or to mercury from unidentified local sources. In the reservoirs, burial of highly contaminated sediments is gradually decreasing the amount of sedimentary mercury available for methylation. In downstream wetlands, however, sedimentary mercury seemed to be more available than that in the reservoirs for physical transport and biogeochemical cycling.
Part A The uppermost Wabaunsee, Admire, Council Grove, and lower Chase Groups of Kansas, Oklahoma, and Nebraska are placed into three third-order depositional sequences: a Gzhelian late-highstand sequence set, a Council Grove transgressive and highstand sequence set, and a Chase transgressive sequence set. Sequences are defined by bounding maximum-exposure surfaces and are placed within the zone of exposure surfaces (typically, stacked paleosols). Conodonts are abundant in open-marine deposits and most marine units have a differing and characteristic faunal make-up. Eleven species are described as new: Streptognathodus binodosus , S. denticulatus , S. elongianus , S. florensis , S. lineatus , S. nevaensis , S. postconstrictus , S. postelongatus , S. robustus , S. translinearis , and S. trimilus . Part B Maximum-marine flooding levels and marine-condensed sections from uppermost Carboniferous and Lower Permian fourth-order (0.1-1 m.y.) depositional sequences of the North American midcontinent reveal a rich stratigraphic succession of species of Streptognathodus and Sweetognathus conodonts that permits high-precision correlation of the Carboniferous-Permian boundary as well as the Asselian-Sakmarian and Sakmarian-Artinskian boundaries. Eleven new species of Streptognathodus are described: Streptognathodus binodosus , S. denticulatus , S. elongianus , S. florensis , S. lineatus , S. nevaensis , S. postconstrictus , S. postelongatus , S. robustus , S. translinearis , and S. trimilus . Seventeen species are redescribed and clarified and include Streptognathodus alius , S. barskovi , S. bellus , S. brownvillensis , S. conjunctus , S. constrictus , S. elongatus , S. farmeri , S. flexuosus , S. fuchengensis , S. fusus , S. invaginatus , S. isolatus , S. longissimus , S. minacutus , S. nodulinearis , and S. wabaunsensis . The correlated level of the Carboniferous-Permian boundary is recognized in the lower part of the Red Eagle Depositional Sequence based on the introduction of Streptognathodus isolatus Chernykh, Ritter, and Wardlaw; Streptognathodus minacutus Barskov and Reimers; Streptognathodus invaginatus Reshetkova and Chernykh; Streptognathodus fuchengensis Zhao; and Streptognathodus nodulinearis Reshetkova and Chernykh. The correlated Carboniferous-Permian boundary occurs in the depositional sequence that represents the maximum-marine highstand of the Council Grove Composite Third Order Sequence. This level represents a significant marine-flooding event that should be correlatable in numerous shelfal sections throughout the world. Although the Asselian-Sakmarian boundary has not been rigorously defined, Sweetognathus merrilli has been informally utilized as a Sakmarian indicator. Due to the ecologically controlled distribution of species of Sweetognathus , we prefer to use a species of Streptognathodus as a defining species. We propose that Streptognathodus barskovi (Kozur) Reshetkova be considered as a potentially defining or ancillary defining species for the Sakmarian Stage. In the North American midcontinent, Streptognathodus barskovi appears in the same depositional sequence with Sweetognathus merrilli in the Eiss (Lower Bader) Depositional Sequence. Historically, Sweetognathus whitei has been used to mark the Sakmarian-Artinskian boundary. In our succession Sweetognathus whitei and Streptognathodus florensis appear in the basal part of the Barneston Depositional Sequence. We suggest that Streptognathodus florensis be further investigated as a possible defining or ancillary defining taxon for the base of the Artinskian Stage. This depositional sequence also forms the maximum-marine highstand of the Chase Third-Order Composite Depositional Sequence suggesting that this level is a significant marine-flooding event that should be widely traceable in numerous shelfal sections.
New biostratigraphic, stratigraphic, and structural data from deformed lower Paleozoic sedimentary units of the Roberts Mountains allochthon (RMA), Independence Mountains, Nevada, have enabled the identification of stratigraphic units within the allochthon that range in age from Late Cambrian through Late Devonian. The McAfee thrust fault emplaced a relatively thick (>200 m) sheet of Ordovician Valmy quartzite (locally termed the McAfee Quartzite) on complexly deformed units of the RMA (locally termed the Snow Canyon Formation) comprised of the Vinini Formation, Elder Sandstone, and Slaven Chert. The rocks were affected by multiple phases of deformation during and after the Devonian-Mississippian Antler orogeny, including: emplacement of the Roberts Mountains allochthon with south-vergent folding and faulting of the upper and lower plate rocks to the Roberts Mountains thrust; emplacement of Upper Mississippian (324 Ma) basalt dikes that cross-cut the upper (allochthonous) and lower (para-autochthonous) plate rocks and south-vergent folds; emplacement of the McAfee Quartzite; and upright north-trending folding after the deposition of Antler overlap rocks. Recognition of this history is required to determine the internal structure and thickness of the allochthon and location of high-angle structures within it that, respectively, may conceal and localize Carlin-type gold deposits in underlying carbonate rocks.
A summary of the stratigraphic occurrence of the Miocene molluscan faunas exposed in marine sandstone seacliffs on the SW Oregon coast. The more common and biostratigraphically significant species are illustrated. - Philip Harris
The units constitute a dominantly clastic sequence of sandstone, conglomerate, mudstone, and shale deposited in (west) to shallow marine (east) environments. Petrologic and paleocurrent data support an interpretation that Blackleaf and lower Frontier debris was derived from different source areas. -from Authors